[spunkets]

"D and L (or S and R) have nothing to do with the rotation of polarized light (+ or -)"

Any molecule that has these assignmnets rotates a polarized beam, because of the asymmetry at the chiral carbon. The interaction is not an absoption, it's a dielectric effect. The 20 std amino acids are all L. Of those, 19 are levorotary(l). I think arginine is (r).

[Senator Bedfellow]

The 20 std amino acids are all L. Of those, 19 are levorotary(l). I think arginine is (r).

Glycine is achiral, the rest are L-amino acids, although D-amino acids do exist in nature.

[grey_whiskers]

Of those, 19 are levorotary(l). I think arginine is (r).

Yikes, say it ain't so, Joe!

I hold in my hand a bottle of L-Arginine which I purchased upon the written recommendation of the late Dr. Atkins (in one of his Atkins Diet books, as an aid to more restful sleep.

You mean I done been flim-flammed on this purchase? :-)

Cheers!

[AndrewC]

The 20 std amino acids are all L.

glycine is achiral. In any case, there is racemization to contend with.

[furball4paws]

Optical rotation is quite complex and is affected by pH and concentration. In addition, the pK of groups like sulfhydryl groups affect the rotation. A big pH change can even shift one from a + rotation to a - rotation.

Here are the rotations, usually at 20 C, but the concentrations and pHs vary because of solubilities:

L-ala +2.8
L-arg +26.9
L-asp +25
L-asn -5.4
L-cys +13
L-cystine -223.4
L-met -8.2
L-glu +31
L-gln +6.1
L-pro -52.6
L-leu -10.8
L-lys +25.9
L-his -39.7
L-thr -28.3
L-ile +11.3
L-val +13.9
L-ser -6.8
L-trp -31.5
L-tyr -10.6
L-phe -35
L-hydroxyproline -76.5
L-ornithine +11.5
L-citrulline +3.7

achiral: glycine, beta-alanine

I'm sure I missed some - list from Merck Index.